K. C. Wright, R. B. Blakestad, C. J. Lobb, W. D. Phillips, G. K. Campbell
We have observed well-defined phase slips between quantized persistent current states around a toroidal atomic (23Na) Bose-Einstein condensate. These phase slips are induced by a weak link (a localized region of reduced superfluid density) rotated slowly around the ring. This is analogous to the behavior of a superconducting loop with a weak link in the presence of an external magnetic field. When the weak link is rotated more rapidly, well-defined phase slips no longer occur, and vortices enter into the bulk of the condensate. A noteworthy feature of this system is the ability to dynamically vary the weak link and hence the critical current, a feature which is difficult to implement in superconducting or superfluid helium circuits.
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http://arxiv.org/abs/1208.3608
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